Magnetic enclosures per se are well known in the art, such as disclosed in the background patents hereinbelow.
U.S. Pat. No. 4,998,976 to Uri Rapoport, discloses a principal permanent magnet and auxiliary permanent magnet means disposed perpendicular to one another.
U.S. Pat. No. 5,014,032 to Guy Aubert recites a cylindrical permanent magnet with a longitudinally induced magnetic field having two annular structures magnetized on the one hand radially with respect to the cylinder axis and on the other hand anti-symmetrically, but is silent about any pole piece for the return of the induction flux from one pole to the other pole.
US Patent Application No. 2005/258833 to Goto Takao et al. discloses use of a plurality of auxiliary magnets that are disposed around main magnets to adjust the interval between the main magnet and the auxiliary magnets and to shape static magnetic fields.
U.S. Pat. No. 5,337,472 to Herbert A. Leupold divulges methods of manufacturing rings, cylinders, hemispheres and spheres having a relatively strong central working field within a central working space.
U.S. Pat. No. 5,621,324 to Kimiharu Ota et al. recite a magnet field generating apparatus comprising a plurality of permanent magnet assemblies disposed continuously around the angular inner circumference of a hexagonal tubular yoke to provide a uniform magnetic field at the center portion of the hollow space inside said permanent magnet assemblies.
U.S. Pat. No. 7,199,689 to Manlio Abele divulges a magnetic structure for generating a uniform magnetic field without the need of an external ferromagnetic yoke, where the magnetic structure serves to carry only part of the return flux of the induction from one pole of the magnetic structure to the other pole.
In U.S. Pat. No. 7,400,147 to Uri Rapoport, there is recited an arrangement of at least six side-magnets and at least two main-magnets.
U.S. Patent No. 2009/0085700 to Jianyu Lian et al. divulges a main assembly of cylindrical geometry with permanent magnets for magnetic field sources that are composed of two regions, a central disk-like portion magnetized substantially along the axial direction and an outer ring-like region magnetized substantially along the radial direction extending axially to form part of a pole.
However, relative to the background art, the embodiments described hereinbelow provide a better ratio of energy stored in magnetic material over magnetic field intensity in a volume of interest.